I received this clock as
a gift in 2002, and in 2015, I was noticing weaker output from the
transmitter and then eventually the outside temperature was not
updating. The WWV radio update (atomic operation) and the
projection of time and temperature are our favorite features.
transmitter is sealed, and I started by sawing with a thin serrated
blade along the case seam. There were no inner attachment
and the case opened up at that point. The front and back view
the board are shown below.
to the back of the board, it is easy to see that the large trace on the
bottom of the image and the square at the top is the ground reference
plane. The processor is clearly encapsulated in the black
and the RF oscillator/transmitter is at the top. This latter
controlled probably by the crystal in the can on the front of the
board. One can also see an antenna on the board traces at the
top-right coupled to by a variable capacitor. It appears (since there
is a crystal) that the capacitor adjust the antenna tuning for maximum
output (and should not affect the frequency). The actual
temperature sensor appears to be a small part in the front middle of
the board that sits in a hole in the front of the small transmitter box.
are fortunately only two traces that cross into the
square ground plane at the top, and one of which is power, the other is
easily determined to be serial output.
These signals are easily accessed by the three
round holes in the middle of the board. These are power (left
back), ground, and serial output (right on
Putting the signal on the serial output line on the scope shows that
the following data protocol (at room temperature).
- There are three groups of data transmissions.
Each last about 85-87 msec with a 24 msec pause between them.
into each group, it is clear that all the 'low' periods are the same
duration, and there are two 'high' durations. This is similar
the Sony SIRCS protocol, and so we can characterize a '1' bit is a long
high and a low, while the '0' bit is a short high and a low.
timing of the '1' is 1.36 msec high, and 920 usec low.
'0' is 560 usec high and 920 usec low. For 50% duty cycle
the average bit time is 1.9 msec, so there are about 46 bits per group.
the board is initially powered up, the chip transmits a packet every
six seconds. After about four minutes, the output rate drops
about one per minute.
the whole assembly (especially the battery contacts) and then
reassembling showed that the transmitter worked fine. As a
soldered a few inches of thin wire-wrap wire to the top terminal on the
back as an
external antenna. This mod appears to make the signal
much better. I suspect the frequency is 433 Mhz, and the
of the half-wave antenna is 13", but I did not make my antenna quite
that long (about 5").